Guardbands are typically used in manufacturing to protect against product and process specification variations. However, if a manufacturer is too conservative in setting the guardband the amount of good products that fail testing is increased. If the guardband is too narrow, the products that go to customers may not function as specified. Two articles that discuss guardbands and the tradeoffs due to guardband placement are The Economics of Guardband Placement, Richard Williams and Charles Hawkins, International Test Conference 1993 and The Effect of Guardbands on Errors in Production Testing, Richard Williams and Charles Hawkins, International Test Conference 1993.
Products, especially, integrated circuits, are designed to be used in a number of applications. Each application often provides a somewhat different set of operating conditions. To insure that the product can work in each of these applications, manufacturing tests must be created to test both for these operating components and the surrounding impact of system components. This could involve a number of variables and parameters. One of the most important variables for processors is the speed which the processor operates in its system environment. Semiconductor manufacturers are constantly changing their designs, application conditions and processes to get faster processors.
Guardbands are determined today in a variety of ways. The easiest approach in developing guardbands is to develop tests that provide for the worst case of every variable. Other approaches include incorporating one of the variables mentioned above (usually test related variables) into determining a guardband, guardbanding reliability wear out mechanisms only, choosing a guardband to satisfy yield targets or not using a guardband at all. For many products, especially integrated circuits that are processors, establishing a guardband using these approaches can lead to sub optimal results.